Construction cement and method for the producing thereof

ABSTRACT

The cement comprises a belite clinker (A) and a second component (B) made up of particles of at least one ceramic material. Preferably this second component has a particle size under 100 nm, and is present in a ratio between 0.2% and 15% by weight of the belite component (A). This cement has the advantages of conventional belite cement and also has better mechanical properties. The process for obtaining a building cement comprises the steps of:  
     (a) producing a belite cement (A) clinker from low lime content fly ash by adding lime (CaO) to the clinker until reaching a CaO/SiO 2  molar ratio greater or equal to 2 and hydrothermally treating the mixture; (b) grinding the obtained clinker; and (c) adding to the clinker a second component (B) made up of at least one ceramic material with a particle size under 100 nm.

FIELD OF THE ART

This invention relates to building cement comprising, as a firstcomponent, belite clinker, and which is suitable for, among others,mortars and concretes. It also relates to a process of obtainingbuilding cement.

STATE OF THE ART

Traditional belite cement primarily consists of the structural β varietyof dicalcium silicate (belite), a compound that is obtained frommixtures of CaCO₃ and clay heated up to 1400° C. This type of cement hascertain properties, distinguished from ordinary Portland cement,necessary for certain applications. First, it has slower hydrationkinetics, so the heat that is released is more gradual, preventingshrinkage problems. This makes it suitable for the mass manufacture oflarge concrete blocks, such as in the case of dams. Secondly, it is amore microstructurally stable cement compared to some aggressiveprocesses taking place in highly alkaline mediums, such as ordinaryPortland cement usually is. Furthermore, the minimum amount of Ca(OH)₂that is produced during its hydration assures its stability againstsulphate attack.

These properties, together with less environmental pollution in terms ofCO₂ emissions, compared to that which occurs during the traditionalPortland cement manufacturing process, and conservation of natural rawmaterials, are promoting the development of research directed towardsobtaining new active belite cements, in the manufacturing processes ofwhich secondary raw materials and environmental-friendly andeconomically viable industrial processes are used, preventing or atleast reducing said environmental problems. In this sense, the use ofindustrial by-products and wastes as alternative raw materials isconsiderably increasing.

Nevertheless, the fact that its hydration rate is low makes it developpoor initial resistances, increasing formwork times since the setting ofthe concrete is slower, and therefore making its large-scale applicationdifficult since construction times are delayed up to unfeasibleextremes. Numerous investigations have been carried out because of thisin the interest of increasing the reactivity of the belite phase (beliteactivation) and achieving better mechanical performance.

The methods used until now for increasing the reactivity of belitecements are basically three in number:

I. Fast Clinker Cooling.

British patent GB2013648, published on Aug. 15, 1979, by RICHARDSCHRADER et al., entitled “A Process for the Manufacture of Cement”,claims a process for obtaining an active belite cement. Themanufacturing process is similar to that of a Portland cement, using rawmaterial formulations appropriate for obtaining the β variety belitephase of dicalcium silicate. Said phase is active by means of the fastcooling of the sintered mixture in a temperature range of 1350° C. and1450° C.

British patent GB2128180, published on Apr. 26, 1984, by RUMPLERKARLHEINZ et al., entitled “Method and apparatus for manufacturingcement of the Belite type”, claims a belite cement clinker sintered at1350° C.-1450° C. followed by fast cooling, preferably with a coolinggradient in the range of 1350° C.-1250° C. as the upper limit and 1000°C.-800° C. as the lower limit.

II. Use of Wastes as Raw Material and Incorporation of StabilizingAgents in the Dicalcium Silicate Lattice: Alkali Metals (Na and K), Feor Al.

U.S. Pat. No. 5,509,962 published on Apr. 23, 1996, by TANG FULVIO J(US), entitled “Cement containing active belite”, claims a cementclinker essentially formed by the belite phase in its alpha variety anda ferrite phase, with a composition of about 0.04-0.13 mol of Na₂O,0.03-0.07 mol of K₂O, 0.09-0.18 mol of Fe₂O₃ and 2.8 mol of dicalciumsilicate. As a raw material, a mixture is used consisting of 70.6%calcareous mineral, 22% rice hull ash, with an 85% SiO₂ purity, and thefollowing commercial agents: 2.4% Fe₂O₃, 2.5% Na₂CO₃ and 2.5% K₂CO₃.Said mixture is ground and pressed, forming cylindrical pellets heatedat 1400° C. for 1 hour. The clinker is ground for 1.5 hours untilobtaining a Blaine fineness of 0.5 m²/g. Two types of cement aremanufactured with this clinker, which contains 90% dicalcium silicate(C₂S) according to Bogue calculations (ASTM C 150-89 Standard): the onecalled FIRH cement with 77% clinker, 7% anhydrite and 16% rice hull ash;and the cement called FIGS with 64.2% clinker, 5.8% anhydrite and 30%slag.

US patent document US2003010257 published on Jan. 16, 2003, by TATSUOIKABATA et al., entitled “Cement clinker, cement composition, method forproducing cement clinker and method for treatment of waste containingalkali component”, claims a cement clinker characterized in that itcontains Al₂O₃ and Fe₂O₃, wherein the weight ratio of Al₂O₃/Fe₂O₃ is0.05-0.62, and alkali components and C₂S wherein the Y content (% byweight) of alkali components and the X content (% by weight) of C₂Ssatisfies the formula: 0.0025X+0.1Y≦Y≦0.01x+0.8. Clinker productionallows the incorporation of alkali components from wastes withconsiderable advantages in increasing the belite hydration rate.

German patent DE3414196, published on Oct. 31, 1985 by TOEPFER PAUL etal., entitled “Alkali-active belite cement”, claims a process forproducing belite cement from a raw material consisting of CaCO₃, SiO₂,Al₂O₃ and Fe₂O₃, with alkali ion addition. The alkalis together with afast cooling improve the properties of the belite cement clinker.

III. Use of Low Lime Content, Hydrothermally Activated Coal CombustionFly Ash as Raw Material, and Synthesis Methods Called Low-EnergyMethods.

WEIMIN JIANG and DELLA M. ROY in Ceramic Bulletin, Vol.71 (4) 1992 pp642-647, synthesized an active low-energy belite cement from a mixtureof CaO and low lime content coal combustion fly ash (FA). The synthesisprocess has several parts. The mixture of CaO, FA and water is firstsubjected to heating at 80° C. for 10 hours, then said mixture is heatedat 200° C. for 4 hours in a pressurized reactor, in which the pozzolanicreaction of the FAs is activated and the precursor phases of the cementare obtained, which are finally dehydrated by heating between 500°C.-900° C. for 4 hours. The final cement contains the belite phaseβ-C2S, mayenite C₁₂A₇ and CaCO₃.

SARA GOÑI et al. in Proc. of Sixth Canmet/ACI International Conferenceon Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete,Bangkok, Ed.: V. M. Malhotra, vol. I, SP-178 pp. 207-224, (1998); andSARA GOÑI et al. in Materials Science of Concrete: The Sidney DiamondSymposium. ISBN: 1-57498-072-6 (1998) pp. 93-108. ANA GUERRERO et al. inCem. Concr. Res., Vol. 29, pp. 1753-1758(1999), disclose synthesizingbelite cement from low lime content FA, based on the work of Weimin andRoy. The main differences of the synthesis process are: omitting thefirst heating at 80° C. for 10 hours of the mixture of FA, CaO andwater; heating the precursor hydrated phases of the cement up to 600° C.at a heating rate of 10° C./min and from 600° C. up to 900° C. at a rateof 5° C./min, and immediately cooling the mixture at room temperature.

DESCRIPTION OF THE INVENTION

This invention has been developed for the purpose of improving themechanical performance of belite cements in order to reduce constructivetimes and thus facilitate its large-scale application. According to thisobjective, the building cement according to this invention ischaracterized by the fact that it comprises a second componentconsisting of particles of at least one ceramic material.

The ceramic material particles have an activating effect on the belitecomponent and allow increasing its hydration rate. The cement accordingto the invention thus maintains all the advantages of the conventionalbelite cement with respect to Portland cement that have been indicated,and it is further appropriate for the large-scale application thereof.

Furthermore, the activation of the belite component of the new cement bymeans of a ceramic material is not susceptible to harmful arid-alkalireactions and therefore is the only process known to date which allowsactivation without the implication of harmful side effects.

The activation mechanism is valid for any type of belite component, i.e.regardless of the synthesis route chosen to obtain it. This implies areduction in the environmental impact because lime decalcification toproduce the major belite phase of the belite cement clinker implies 33%less CO₂ emissions.

In one embodiment, said ceramic material shows a particle size under 100nm, and more preferably between 5 nm and 50 nm, since particle sizegreatly affects the activating effect of the belite component.Furthermore, it has been verified that belite activation does not occurwith particle sizes over 100 nm.

It is believed that, with respect to the activation mechanism,nanomaterials, either nanosilica or nanoalumina, react directly with theC—S—H gel. They thus act as nucleation “points” for gel growth and thusaccelerate their formation. More specifically, it is thought thatnanoparticle addition promotes the growth of silica chains in the gel,giving therefore a gel with a lower Ca/Si ratio and therefore morestable and microstructurally more complex (with less defects in themanner of vacancies and discontinuities). Thus high initial resistancesare obtained, because the C—S—H gel is the major component of thehydrated cement matrix and is responsible for mechanical resistance.

According to advantageous embodiments, the cement comprises a proportionof said second component between 0.2% and 15% by weight of the belitecomponent. Improvements in mechanical resistance at 7 days of up to 200%with respect to belite component resistance have been obtained withthese proportions without ceramic nanomaterial. In specific exampleswhich have given very good results the cement comprises a proportion ofsaid second component between 2% and 10% by weight of the belitecomponent.

Preferably, the second component comprises particles of at least onesilica material (SiO₂) and/or at least one alumina material (Al₂O₃).

In one embodiment, the second component comprises a colloidal dispersionof ceramic material particles. The fact that it is to be found in theform of a colloidal dispersion stabilises the nanomaterial, preventingits particles from clustering in larger grains, and therefore allowingthe particles to have a greater reactivity and a greater activatingeffect.

Optionally, the second component may comprise particles made of twodifferent ceramic materials which may have different particle sizes.

According to particularly advantageous embodiments of the invention, thebelite component is obtained from low lime content fly ash, and with lowenergy synthesis methods, with synthesis temperatures of approximately800° C.

The use of a belite component of these characteristics means a clearreduction in production costs, due to the drastic reduction in synthesistemperature (800° C. versus 1450° C.) and the reduction in grindingneeds; furthermore, from the ecological point of view, CO₂ emissions arereduced during the oven process and an industrial process residue isused as the raw material, which implies a reduction in natural resourceexploitation and a resulting reduction in quarry exploitation costs.

Thus, the greater technological, economical and environmental reach ofthe present invention would be achieved with a belite component obtainedfrom hydrothermally activated fly ash as a raw material and so-calledlow energy synthesis methods.

According to a second aspect, the present invention refers to a processfor obtaining building cement characterised in that it comprises thesteps of:

(a) producing a belite cement clinker from low lime content fly ash,providing lime (CaO) to the clinker until reaching a CaO/SiO₂ molarratio approximately equal to 2 and hydrothermally treating the mixture;

(b) grinding the obtained clinker; and

(c) adding to the clinker a second component (B) formed by at least oneceramic material with a particle size under 100 nm.

The belite clinker cement is preferably obtained with a low energysynthesis method.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A cement according to the invention presents a first component which isa belite clinker A and a second component B made up of a ceramicnanomaterial. Nanomaterial in the present document is understood as amaterial with some of its dimensions under 100 nanometers; and ceramicmaterial is understood as a material made up by at least one metalelement and one non-metal element, such that the interatomic bonds areof a predominantly ionic character. Typical examples of ceramiccompounds would be NaCl, MgO, FeO, ZnS, Al₂O₃, SiO₂, Fe₂O₃, BaTiO₃, etc.

In one embodiment of the invention, a belite cement is used as componentA which is obtained from fly ash from the combustion of low lime contentcoal as raw material for obtaining the clinker. This raw material needsan additional contribution of lime (CaO) in order to reach a CaO/SiO₂molar ratio approximately equal to 2 and to obtain a cement with theappropriate composition.

Belite component A is preferably obtained by means of low energysynthesis methods such as those described in the articles described inthe introduction, with a low synthesis temperature (800° C. versus the1450° C. for Portland cement and the 1350° C. for a traditional belitecement), a lower need for grinding the clinker since at said temperature(800° C.) phase fusion is not reached, and a low need for grinding theraw material since this is mainly fly ash with a great surface area.Therefore the energetic and environmental impact of the productionprocess of this cement is clearly less than that of a normal Portlandcement.

Minor amounts of Ca(OH)₂, are produced during hydration, which assures agood durability of the mortars and concretes manufactured with the newcement in the aggressive environments in which Ca(OH)₂ may sufferexpansive reactions, such as is the case in attacks with sulphates.

The ceramic nanomaterial (component B) performs the function of beliteclinker A hydration reaction activator. In preferred embodiments of theinvention silica (SiO₂) and alumina (Al₂O₃) ceramic nanomaterials withparticle sizes comprised between 5 and 50 nanometers may be used;component B is more reactive the smaller its particle size is.

Ceramic nanomaterial B may be added in the form of a colloidaldispersion, such that its particles are prevented from clustering and agreater activating effect is favoured.

Component proportions in the mixture forming the new cement determinesits mechanical properties, which at early ages (<28 days) are clearlygreater than those of belite cement component A (i.e. withoutnanomaterial) and comparable to those of a normal Portland cement, andparticularly a cement of class cem I 32.5. With proportions of componentB comprised between from 0.2% to 15% by weight of component A,improvements in mechanical strength are obtained at 7 days of up to 200%with respect to the resistance of component A without nanomaterial.

The process for obtaining cement paste, mortar, etc. with the cementsaccording to the invention depend on the product to be obtained, but itcan be said that in general a greater water/cement ratio is used,generally over 0.5% (although this depends on the type of startingbelite cement), and that a mixing time exceeding 4 minutes (includingresting times) is used and with a typical reference sequence such as:

-   -   from approximately 1.5 minutes to 2.5 minutes mixing between 100        and 1000 rpm;    -   from approximately 30 seconds to 1 minute rest;    -   from approximately 1.5 minutes to 2.5 minutes mixing between 100        and 1000 rpm;    -   optionally, from approximately 30 seconds to 1 minute rest and        approximately 1.5 minutes mixing between 100 and 1000 rpm;    -   2 days in the mould

Processes for obtaining different products using cements according tothe invention are described in detail in the following examples, andtheir properties are analysed by comparing them to those of conventionalbelite cement.

EXAMPLES

Introduction

For all the examples set forth below a belite cement (component A) hasbeen used that was obtained from hydrothermally activated fly ash fromlow lime content coal combustion as raw material, and so-called lowenergy synthesis methods (such as mentioned at the end of the “State ofthe Art” section). This cement will be hereinafter called CBCV.

The chemical and mineralogical composition of the fly ash used as rawmaterial appears in Table 1 and FIG. 1. The ash complies with therequirements for type F of the ASTM classification: SiO₂+Al₂O₃+Fe₂O₃contents exceeding 70% and a low lime content, as can be seen inTable 1. TABLE 1 Chemical composition of fly ash (% by weight) BETDensity *L.I. *I.R. CaO SiO₂ Al₂O₃ Fe₂O₃ MgO Na₂O K₂O (m²/g) (g/cc) 5.60.3 4.65 48.8 26.8 7.45 1.9 0.67 3.65 0.75 2.11*L.I. = Loss on ignition*I.R. = Insoluble Residue

The main crystalline phases are: α-SiO₂ (α-quartz), α-Fe₂O₃ (hematite)and Al₆Si₂O₁₃ (mullite). Regarding the amorphous halo, between 15 and 352θ corresponds to the starting ash amorphous silica.

FIG. 1 shows an X-ray diffractogram of the starting ash, in which M ismullite, H is hematite and Q is α-quartz.

An addition of commercial lime is necessary for cement synthesis so thata Ca/Si molar ratio of 2 is reached in order to obtain the belitecement. The ash, lime and water mixture is hydrothermally treated at200° C. and a pressure of 1.24 MPa for 4 hours, with constant stirring.After this time, the reactor is cooled and the solid is filtered anddried at a temperature of 80° C. the dry product is subsequently heatedup to 600° C. at a heating speed of 10° C./min and from 600° C. up to800° C. at a speed of 5° C./min; thus obtaining the fly ash belitecement clinker.

This cement will be component A of the examples set forth below.

The crystalline solid phases of component A have been characterized byX-ray diffraction. FIG. 2 shows the X-ray diffraction analysis forcomponent A. In the diffractogram, C represents CaCO₃, β representsβ-Ca₂SiO₄, α represents α′-L-Ca₂SiO₄,

represents C₃A, l represents CaO, and M represents C₁₂A₇. The majorcrystalline phases are the α′-L and β-C₂S varieties of dicalciumsilicate together with greater amounts of mayenite (C₁₂A₇), C₃A(tricalcium aluminate), free CaO and calcite (CaCO₃).

The different examples chosen to illustrate the invention are detailedbelow.

Example 1

Ecoefficient Cement from FABC as Component A and Nanoalumina Powder asComponent B

Component Description

Component A has been described in the introduction to the “Examples”section. Component B is a commercial type of nanoalumina Al₂O₃ (Nyacol®AL20SD) with the characteristics provided by the manufacturer shown inTable 2. TABLE 2 Reactive Primary particle size nanomaterial (%) Medium(nm) Appearance >80 Dry powder 50 nm White powder

Due to the absence of a dispersive medium, the particulate nanoaluminain this Example tends to agglomerate in grains with sizes ranging from0.1 microns to 1 micron. Mixing procedure

Trial mixes of 1×1×6 cm of mortar with a water/(component A) ratio of0.8 and a sand/(component A) ratio of 3 were manufactured. Three batcheswhere made with these reference amounts, producing six trial mixes withthe aforementioned dimensions for each one. The first batch did not havecomponent B, which will be taken as a reference to estimate the percentof improvement achieved by adding component B. In the second trial mixcomponent B was added in 3% by weight of component A and in the third in9% by weight of component A.

All the trial mixes were carried out in the following manner. ComponentA and component B were manually homogenized in a container with ashovel. Then the sand was tipped into the mixture and a manualhomogenization was again carried out. Once this initial mixture wasready, distilled water was poured into it and it was mixed by means ofan electronic mixer and the following sequence: 2 minutes at 750 rpm, 1minute rest, 2 minutes at 750 rpm, 1 minute rest and 1 minute at 750rpm. After mixing the mixture was poured into prismatic moulds with theaforementioned dimensions (1×1×6 cm) and it was compacted on acompaction table by 60 successive rappings. Afterwards, the mixtures areallowed to cure until breaking time in a climatic chamber with arelative humidity over 90% and a temperature of 21±2° C. The sampleswere demoulded 48 hours after mixing.

Mechanical Resistance

Resistance values at 7 and 28 days of the mixtures manufacturedaccording to the previously specified procedure are presented in Table3. TABLE 3 Example 1 7 days 28 days Cem I 32.5 ≧16 ≧32.5 Comp. A 4.02 ±0.26  8.46 ± 0.26 Comp. A + 3% Comp. B 7.86 ± 0.43 15.68 ± 0.14  96% 85% Comp. A + 9% Comp. B 9.74 ± 0.11 18.51 ± 0.69 142% 119%

Table 3 shows mechanical resistance to compression (MPa). The valuesdemanded by the UNE-196-1 regulation for a normal Portland cement ofclass cem I 32.5 are shown in the first row. The percent of improvementfor each mixture of component A with component B regarding the value ofcomponent A without component B is shown (separated by a dotted line).

As can be seen the introduction of component B in low percentages withrespect to component A means doubling the resistances both at 7 and at28 days.

Hydration and Durability Features

Hydration of the cement obtained in this Example 1 shows severalessential features which may be inferred from an X-ray diffraction study(FIG. 3) of the hydration products. FIG. 3 shows an X-ray diffractogramof hydration at 7 days of component A and of component A plus componentB in a proportion by weight of 3 and 9%. The main peak of the belitephases of component A has been framed (FIG. 2) in order to stress itsconsumption as the concentration of component B increases.

As can be seen in FIG. 3, the essential features of the cement ofExample 1 are:

-   -   1. The speed of hydration with respect to a normal belite        cement, such as is clear from the mechanical resistance (double        at 7 days), and as can be seen in the X-ray spectrums for the        hydrated product (component A+component B), which are shown in        FIG. 3. This figure shows the main peak of the belite phases        (2θ˜33°) present in component A (FIG. 2) in order to stress the        consumption of these phases when incorporating component B.    -   2. The absence of ettringite, the main peaks of which would be        found in 2θ·9°, 16°, 23° and 32° and which do not appear in the        spectrums studied.    -   3. The presence of small amounts of portlandite (Ca(OH)₂) (4% at        3 days after hydration, an amount which decreases with time and        which can no longer be seen in the diagrams at 7 days shown in        FIG. 3) compared to the 18% portlandite generated in the        hydration of a Portland cement. This is a feature of component A        which is not negatively affected by its mixture with component        B.    -   4. The major presence of non-crystalline phases formed by the        hydration products of Ca and Si; Ca, Si and Al; Si and Al; and        Ca and Al. All this can be inferred from the presence of very        wide peaks on a bulging spectrum (amorphous halo from 2θ˜20°).

It can be inferred from the last three features mentioned that themortars and concretes manufactured with the new cement will show gooddurability in aggressive environments, such as in the case of attacks bysulphates. Thus, the mixture component A and component B proposed inthis invention maintains the durability properties of component A,whereas obtaining a product with notable mechanical properties at anearly age.

Example 2

Ecoefficient Cement from FABC as Component A and Nanoalumina in aColloidal Dispersion as Component B

Component A has been described in the introduction to the “Examples”section. Component B is a commercial type of nanoalumina Al₂O₃ (Nyacol™AL20) with the characteristics provided by the manufacturer shown inTable 4. TABLE 4 Reactive Primary particle size nanomaterial (%) Medium(nm) Appearance 20 Water 50 nm Milky

In contrast to the nanoalumina in Example 1, the nanoalumina of thecurrent Example is shown as a colloidal dispersion, i.e. aluminaparticles of a mean size of 50 nm dispersed in a liquid medium, which inthis case is water. The nanometric character of the active particles ofcomponent B is thus preserved.

Mixing Process

Trial mixes of 1×1×6 cm of mortar with a water/(component A) ratio of0.8 and a sand/(component A) ratio of 3 were manufactured. Three batcheswhere made with these reference amounts, producing six trial mixes withthe aforementioned dimensions for each one. The first batch did not havecomponent B, which will be taken as a reference to estimate the percentof improvement achieved by adding component B. In the second trial mixcomponent B was added in 3% by weight of component A and in the third in9% by weight of component A. Knowing that the nanoalumina content incomponent B is 20% (TABLE 4), the percent of active ingredient(nanoalumina) is less than that of the product used in this example ascomponent B (Nyacol® AL20).

All the trial mixes were carried out in the following manner. ComponentA and the sand were manually homogenized in a container with a shovel.Distilled water was mixed with component B in another container such asto achieve a water/(Component A) ratio of 0.8. The contribution in waterof component B must be taken into account (80% of component B is water,TABLE 4). This mixture was homogenized by stirring for 5 minutes. Afterthis initial step the mixture of water and component B was poured on themixture of component A and sand and mixing, moulding and curing wascarried out following the same sequence as that set forth in Example 1.

Mechanical Resistance

Resistance values at 7 and 28 days of the mixtures carried out accordingto the aforementioned procedure are shown in Table 5. TABLE 5 Example 27 days 28 days Cem I 32.5 ≧16 ≧32.5 Comp. A 4.02 ± 0.26 8.46 ± 0.26Comp. A + 3% Comp. B 6.29 ± 0.24 16.02 ± 0.99  (0.6% nanoalumina) 56% 89% Comp. A + 9% Comp. B 7.41 ± 0.28 18 ± 1  (1.8% nanoalumina) 84%113%

Table 5 shows mechanical resistance to compression (MPa). The valuesdemanded by the UNE-196-1 regulation for a normal Portland cement ofclass cem I 32.5 are shown in the first row. The percent of improvementfor each mixture of component A with component B regarding the value ofcomponent A without component B is shown (separated by a dotted line).

As can be seen the introduction of component B in low percentages withrespect to component A means doubling the resistances both at 7 and at28 days (at this age, with 9% of component B the resistance value isactually doubled).

A comparison between these results and those obtained in Example 1 showsan apparently greater effectiveness of component B in Example 1 withrespect to the present Example. However, it must be taken into accountthat component B in the present example contains at least 4 times lessnanoalumina (20% concentration, TABLE 4) than component B in Example 1.Therefore, a greater activation of component A of the invention isachieved with a smaller amount of active ingredient (nanoalumina in thiscase). This is due to the fact that component B in Example 2 maintainsits nanometric character (size under 100 nm) and thus a greaterreactivity given that the nanoalumina is stabilized by the water and isnot clustered in larger grains, such as occurs with the nanoalumina inExample 1. All this will have important consequences in the hydration,as discussed below.

Hydration and Durability Features

Hydration of the present invention, according to this Example 2, has thesame features as those shown in Example 1 (speed of hydration, absenceof ettringite and portlandite and presence of an amorphous halo),although with some quantitative differences worth mentioning:

-   -   1. The same as in Example 1, the setting reaction kinetics are        accelerated by the presence of component B, such as clearly seen        by its mechanical resistance (almost double at 7 days), and as        can be seen in the X-ray spectrums for the reference hydrated        product (only component A) and for the hydrated product        (component A+component B) shown in FIG. 4, which shows an X-ray        diffractogram of the hydration at 7 days for component A and        component A plus component B in a 9% proportion by weight. The        main peak of the belite phases (2θ˜33°) present in component A        (FIG. 2) have been framed in order to stress the consumption of        these phases when incorporating nanoalumina. However, it is        worth stressing, in contrast to Example 1 (FIG. 3), a greater        reduction of the belite phase peaks (FIG. 2) for the same amount        of component B. Although it is true that the amount of        nanoalumina present in component B of the present Example is        lower than that of Example 1, it is also true that the        nanoalumina of component B in the present example maintains its        nanometric character by being in a colloidal dispersion, and        thus shows a greater reactivity, as is demonstrated in the X-ray        diagrams in FIG. 4. Note that the intensity of peak 2θ˜33° is        reduced practically in half (0.5 factor) for 9% of component B,        or 1.5% of nanoalumina, whereas the same peak in FIG. 3 was        reduced by a 0.75 factor. For all this, it is worth stressing        the crucial role of the nanometric character of the active        ingredient of component B, and which can even have important        repercussions regarding exploiting the present invention.    -   2. The amorphous halo is slightly more pronounced in this case        than in Example 1. Also, a peak around 2θ˜7° corresponding to a        crystalline phase of a hydration product with Ca, Si and Al        (platlingite), present in FIG. 3, is not seen in FIG. 4. All        this leads to assume a greater presence of non-crystalline        phases formed by hydration products of Ca and Si; of Ca, Si and        Al; and of Si and Al and of Ca and Al.

From all of this a high durability may be inferred, as mentioned alreadyin Example 1, by maintaining the same features. Furthermore, thequantitative differences mentioned lead to assume a greater qualitymicrostructure in the present example than in Example 1. That is, at thesame age of 7 days in Example 2 there is more hydrated cement (morebelite consumed, as can be seen in the lower characteristic peak 2θ˜33°)and therefore a better formed microstructure.

Example 3

Ecoefficient Cement from FABC as Component A and Powder Nanosilica asComponent B

Component A has been described in the introduction to the “Examples”section. Component B is a commercial type of nanosilica (Nyacol® Nyasil5) with the characteristics provided by the manufacturer shown in Table6. TABLE 6 Reactive Primary particle size nanomaterial (%) Medium (nm)Appearance >96 Dry powder 5 nm White powder

Due to the absence of a dispersive medium, the particular nanosilica inthis example tends to cluster in grains with variable sizes around 1micron.

Mixing Process

Trial mixes of 1×1×6 cm of cement paste (without sand) with awater/(component A) ratio of 0.8 were manufactured. Two batches weremade with these reference amounts, producing 6 trial mixes with theaforementioned dimensions for each one. The first batch did not containcomponent B, which will be taken as a reference for estimating thepercent improvement achieved by adding component B. In the second trialmix component B was added in 6% by weight of component A.

All the trial mixes were carried out in the following manner. ComponentA and component B were manually homogenized in a container with ashovel. Once this initial mixture was ready, distilled water was pouredon said mixture and it was mixed by means of an electronic mixer and thefollowing sequence: 1 minute and 30 seconds at 750 rpm, 1 minute restand 1 minute and 30 seconds at 750 rpm. After mixing the mixture waspoured in prismatic moulds with the aforementioned dimensions (1×1×6 cm)and it was compacted on a compaction table by 60 successive rappings.Afterwards, the mixtures are allowed to cure until the breaking time ina climatic chamber with a relative humidity over 90% and a temperatureof 21±2° C. The samples were demoulded 48 hours after mixing.

Mechanical Resistance

Resistance values at 7 days for the mixtures carried out according tothe aforementioned procedure are shown in Table 7. TABLE 7 Example 1 7days Comp. A 3.41 ± 0.27 Comp. A + 6% Comp. B 5.98 ± 0.52 75%

Table 7 shows mechanical resistance to compression (MPa). The percent ofimprovement for the mixture of component A with component B regardingthe value of component A without component B is shown (first row).

As can be seen the introduction of component B in low percentages withrespect to component A means considerably increasing initial resistance(about 75%).

Hydration and Durability Features

Hydration of the cement of this Example 3 has the same features as thoseshown in Examples 1 and 2 (hydration speed, absence of ettringite andportlandite and presence of an amorphous halo). FIG. 5 shows an X-raydiffractogram for hydration at 7 days of component A and for component Aplus component B in a 6% proportion by weight. The main peak for thebelite phases of component A (FIG. 2) has been framed to stress itsconsumption when adding component B. It is worth mentioning a greaterbelite consumption with respect to Example 1, as evidenced by the lowerheight of peak 2θ˜33° in the case of the component A and component Bmixture (lower panel in FIG. 5) versus that of component A withoutcomponent B (upper panel in FIG. 5). Furthermore, not including aluminawill not give rise to non-crystalline phases formed by hydrationproducts containing Al, being mainly Ca and Si compositions.

From all of this a high durability may be inferred, as mentioned alreadyin Examples 1 and 2, by maintaining the same durability features ascomponent A.

Example 4

Ecoefficient Cement from FABC as Component A and Colloidal Nanosilica asComponent B

Component A has been described in the introduction to the “Examples”section. Colloidal nanosilica has been used as component B, but with twodifferent particle sizes. That which will be called component B1 is acommercial type of nanosilica (Levasil® Grade 100) and that which willbe called component B2 is another type of commercial nanosilica(Levasil® Grade VPAC 4038) with the characteristics provided by themanufacturer shown in Tables 8-1 and 8-2, respectively. TABLE 8-1Reactive Primary particle size nanomaterial (%) Medium (nm) Appearance45 Water 30 nm Milky

TABLE 8-2 Reactive Primary particle size nanomaterial (%) Medium (nm)Appearance 30 Water 15 nm Transparent, slightly opalescent liquid

In contrast to the nanosilica of Example 3, the nanosilica of thecurrent Example is shown as a colloidal dispersion, i.e. silicaparticles with a mean size of 30 and 15 nm, respectively, dispersed in aliquid medium, which in this case is water. Thus, the nanometriccharacter of the active particles of component B is maintained and thereis no clustering.

Mixing Process

Trial mixes of 1×1×6 cm of cement paste (without sand) with awater/(component A) ratio of 0.8 were manufactured. Two batches weremade with these reference amounts, producing 6 trial mixes with theaforementioned dimensions for each one. The first batch did not containcomponent B, which will be taken as a reference for estimating thepercent improvement achieved by adding component B. In the second trialmix component B was added in 6% by weight of component A. Taking intoaccount that the nanosilica content in component B1 is 45% (TABLE 8-1),and that the nanosilica content in component B2 is 30% (TABLE 8-2), thepercent of active ingredient (nanosilica) is lower than that of theproduct used in this example as component B (2.7% Levasil® Grade 100 asB1 and 1.8% Levasil® Grade VPAC 4038 as B2).

All the trial mixes were carried out in the following manner. Distilledwater was mixed with component B in another container such as to achievea water/(Component A) ratio of 0.8. The contribution in water ofcomponent B must be taken into account (55% of component B1 is water,8-1, and 70% of component B2 is water, TABLE 8-2). Once this initialmixture was ready, component A was poured over said mixture and it wasmixed by means of an electronic mixer and the following sequence: 1minute and 30 seconds at 750 rpm, 1 minute rest and 1 minute and 30seconds at 750 rpm. After mixing the mixture was poured into prismaticmoulds with the aforementioned dimensions (1×1×6 cm) and it wascompacted on a compaction table by 60 successive rappings. Afterwards,the mixtures are allowed to cure until breaking time in a climaticchamber with a relative humidity over 90% and a temperature of 21±2° C.The samples were demoulded 48 hours after mixing.

Mechanical Resistance

Resistance values at 7 days for the mixtures carried out according tothe aforementioned procedure are shown in Table 9. TABLE 9 Example 4 7days Comp. A 3.41 ± 0.27 Comp. A + 6% Comp. B1 8.71 ± 0.51 (2.7%nanosilica) 155% Comp. A + 6% Comp. B2 10.1 ± 0.6  (1.8% nanosilica)196%

Table 9 shows the mechanical resistance to compression (MPa). Thepercent of improvement for the mixture of component A with component Bregarding the value of component A without component B is shown (firstrow).

As can be seen the introduction of component B in low percentages withrespect to component A means almost tripling the resistance valueobtained only with component A (-200% for the mixture with componentB2).

A comparison of these results with those obtained in Example 3 shows agreater effectiveness of the two components B of the present Examplewith respect to Example 3. As in the case of Example 2 with respect toExample 1, the fact that the components B of this Example maintain theirnanometric character due to their being in a dispersion (there are noclusters) has a strong impact in the increase in final mechanicalproperties. On the other hand, with this example the influence of theparticle size is also shown. In fact, with a greater amount ofnanosilica in component B1 than in component B2 there is less resistanceto compression. This is due to the increase in reactivity with thereduction in particle size (30 nm in B1 and 15 nm in B2). The same canbe said if comparing with respect to examples 1 and 2, although in thiscase the different nature of the addition must be taken into account andthe fact that in Examples 1 and 2 it is cement paste and not mortar thatis being worked with.

Hydration and Durability Features

Hydration of the material obtained in Example 4 has the same features asthose in Examples 1, 2 and 3 (hydration speed, absence of ettringite andportlandite and presence of an amorphous halo). It has similar featuresto those of Example 3 regarding non-crystalline phase compositioninsofar as that they will not contain Al. On the other hand, a similarconsumption of belite as that in Example 3 is observed. However, thefact that greater mechanical resistance is obtained suggests thepresence of more polymerized non-crystalline phases, which unfortunatelycannot be detected by X-ray diffraction. In any case, this fact, as iswell-known, will not negatively affect durability, but on the contrary,it is also a sign of greater hydration speed.

FIG. 6 shows the X-ray diffractogram of hydration at 7 days forcomponent A and component A plus component B in a proportion by weightof 9%. The main peak of the belite phases of component A (FIG. 2) hasbeen framed to stress its consumption with the addition of component B.

Although some specific embodiments of the present invention have beendescribed a person skilled in the art will be able to introduce variantsand modifications depending on the particular requirements of each case,and to substitute some elements for other technically equivalent ones,for example, although a cement made essentially from a belite clinkerand a ceramic component has been described herein, it is clear that thecement and each of its components may also contain conventionaladditives, particularly super plasticizing agents, and other elementswithout leaving the scope of protection defined by the attached claims.

1. A building cement comprising as a first component a belite clinker(A) and a second component (B) comprising particles of at least oneceramic material, wherein said ceramic material has a particle size lessthan 100 nm.
 2. (canceled)
 3. The cement according to claim 1, whereinsaid ceramic material has a particle size of between 5 nm and 50 nm. 4.The cement according to claim 1, wherein said cement comprises 0.2% and15% by weight of said second component (B) based on the weight of thebelite clinker (A).
 5. The cement according to claim 4, wherein saidcement comprises 2% and 10% by weight of said second component (B) basedon the weight of the belite clinker (A).
 6. The cement according toclaim 1, wherein said second component (B) comprises particles of atleast one silica material (SiO₂).
 7. The cement according to claim 1,wherein said second component (B) comprises particles of at least onealumina material (Al₂O₃).
 8. The cement according to claim 1, whereinsaid second component (B) comprises a colloidal dispersion of ceramicmaterial particles.
 9. The cement according to claim 1, wherein saidsecond component comprises particles of two different ceramic materials.10. The cement according to claim 9, wherein said two different ceramicmaterials have a different particle size.
 11. The cement according toclaim 1, wherein the belite clinker (A) is obtained from low limecontent fly ash.
 12. The cement according to claim 11, wherein thebelite clinker (A) is obtained using a low energy synthesis method, anda synthesis temperature of approximately 800° C.
 13. The cementaccording claim 1, additionally comprising a superplasticizing agent.14. A process of obtaining a building cement, comprising the steps of:(a) producing a belite clinker (A) from low lime content fly ash byadding lime (CaO) to the ash until reaching a CaO/SiO₂ molar ratioapproximately equal to 2, and hydrothermally treating the resultingmixture; (b) grinding the obtained clinker; and (c) adding to theclinker a second component (B) comprising at least one ceramic materialhaving a particle size less than 100 nm.
 15. The process according toclaim 14, wherein the belite clinker (A) is obtained with using a lowenergy synthesis method.
 16. (canceled)
 17. A paste comprising a binderand water, wherein the binder comprises a cement according to claim 1.18. A mortar comprising a binder, an aggregate and water, wherein thebinder comprises a cement according to claim
 1. 19. A concretecomprising a binder, an aggregate and water, wherein the bindercomprises a cement according to claim 1.